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Problems for Chapter 2
PROBLEM 1
Draw good diagrams of saturated hydrocarbons with seven carbon atoms having (a) linear, (b) branched, and (c) cyclic structures. Draw molecules based on each framework having both ketone and carboxylic acid functional groups in the same molecule.
PROBLEM 2
Draw for yourself the structures of amoxicillin and Tamiflu shown on page 10 of the textbook. Identify on your diagrams the functional groups present in each molecule and the ring sizes. Study the carbon framework: is there a single carbon chain or more than one? Are they linear, branched, or cyclic?
PROBLEM 3
Identify the functional groups in these two molecules
2 Problems to accompany Organic Chemistry
PROBLEM 4
What is wrong with these structures? Suggest better ways to represent these molecules
PROBLEM 5
Draw structures for the compounds named systematically here. In each case suggest alternative names that might convey the structure more clearly if you were speaking to someone rather than writing. (a) 1,4-di-(1,1-dimethylethyl)benzene (b) 1-(prop- 2 - enyloxy)prop- 2 - ene (c) cyclohexa-1,3,5-triene
PROBLEM 6
Translate these very poor structural descriptions into something more realistic. square planar carbon atoms or any other bond angles of 90°. (a) C 6 H 5 CH(OH)(CH 2 ) 4 COC 2 H 5 (b) O(CH 2 CH 2 ) 2 O (c) (CH 3 O) 2 CH=CHCH(OCH 3 ) 2
PROBLEM 7
Identify the oxidation level of all the carbon atoms of the compounds in problem 6.
Problems for Chapter 3
PROBLEM 1
Assuming that the molecular ion is the base peak (100% abundance) what peaks would appear in the mass spectrum of each of these molecules: (a) C 2 H 5 BrO (b) C 60 (c) C 6 H 4 BrCl In cases (a) and (c) suggest a possible structure of the molecule. What is (b)?
PROBLEM 2
Ethyl benzoate PhCO 2 Et has these peaks in its 13 C NMR spectrum: 17.3, 61.1, 100 150 (four peaks) and 166.8 ppm. Which peak belongs to which carbon atom? You are advised to make a good drawing of the molecule before you answer.
PROBLEM 3
proved exceptionally difficult to solve t difficult? Could anything be gained from the 13 C or 1 H NMR? What information could be gained from the mass spectrum and the infra red?
PROBLEM 4
The solvent formerly used in some correcting fluids is a single compound C 2 H 3 Cl 3 , having 13 C NMR peaks at 45.1 and 95.0 ppm. What is its structure? How would you confirm it spectroscopically? A commercial paint thinner gives two spots on chromatography and has 13 C NMR peaks at 7.0, 27.5, 35.2, 45.3, 95.6, and 206.3 ppm. Suggest what compounds might be used in this thinner.
PROBLEM 5
H stretch in the infrared (i.e. without hydrogen bonding) comes at about 3600 cm 1. What is the reduced mass () for O H? What happens to the reduced mass when you double the mass of each atom in turn, i.e. what is for O D and what is for S H? In fact, both O D and S H stretches come at about 2,500 cm 1. Why?
Problems for Chapter 3 Determining organic structures 7
PROBLEM 9
How many signals would you expect in the 13 C NMR spectrum of these compounds?
8 Problems to accompany Organic Chemistry
PROBLEM 10
When benzene is treated with tert - butyl chloride and aluminium trichloride, a crystalline product A is formed that contains only C and H. Mass spectrometry tells us the molecular mass is 190. The 1 H NMR spectrum looks like this: If crystals of A are treated again with more tert - butyl chloride and aluminium chloride, a new oily compound B may be isolated, this time with a molecular mass of 246. Its 1 H NMR spectrum is similar to that of A , but not quite the same: What are the two compounds? How many signals do you expect in the 13 C NMR spectrum of each compound? Compound A Compound B
10 Problems to accompany Organic Chemistry
PROBLEM 6
Draw detailed structures for these molecules and predict their shapes. We have deliberately made non-committal drawings to avoid giving away the CO 2 , CH 2 =NCH 3 , CHF 3 , CH 2 =C=CH 2 , (CH 2 ) 2 O
PROBLEM 7
Draw the shapes, showing estimated bond angles, of the following molecules: (a) hydrogen peroxide, H 2 O 2 (b) methyl isocyanate CH 3 NCO (c) hydrazine, NH 2 NH 2 (d) diimide, N 2 H 2 (e) the azide anion, N 3
PROBLEM 8
Where would you expect to find the lone pairs in (a) water, (b) acetone (Me 2 C=O), and (c) nitrogen (N 2 )?
Problems for Chapter 5
PROBLEM 1
Each of these molecules is electrophilic. Identify the electrophilic atom and draw a mechanism for a reaction with a generalized nucleophile Nu , giving the structure of the product in each case.
PROBLEM 2
Each of these molecules is nucleophilic. Identify the nucleophilic atom and draw a mechanism for a reaction with a generalized nucleophile E+, giving the structure of the product in each case.
PROBLEM 3
Complete these mechanisms by drawing the structure of the product(s).
Problems for Chapter 5 Organic reactions 13
PROBLEM 7
These three reactions all give the products shown, but not by the mechanisms drawn! For each mechanism, explain what is wrong, and draw a better one.
PROBLEM 8
In your corrected mechanisms for problem 7, explain in each case which orbital is the HOMO of the nucleophile and which orbital is the LUMO of the electrophile.
PROBLEM 9
Draw a mechanism for the following reaction. (This is harder, but if you draw out the structures of the reactants first, and consider that one is an acid and one is a base, you will make a good start.)
16 Problems to accompany Organic Chemistry
PROBLEM 4
There are three possible products from the reduction of this compound with sodium borohydride. What are their structures? How would you distinguish them spectroscopically, assuming you can isolate pure compounds?
PROBLEM 5
The triketone shown here i amino acids. It exists in aqueous solution as a hydrate. Which ketone is hydrated and why?
PROBLEM 6
This hydroxyketone shows no peaks in its infrared spectrum between 1600 and 1800 cm 1 , but it does show a broad absorption at 3000 3400 cm 1. In the 13 C NMR spectrum there are no peaks above 150 ppm but there is a peak at 110 ppm. Suggest an explanation.
Problems for Chapter 6 Nucleophilic addition to the carbonyl group 17
PROBLEM 7
Each of these compounds is a hemiacetal and therefore formed from an alcohol and a carbonyl compound. In each case give the structures of the original materials.
PROBLEM 8
Trichloroethanol my be prepared by the direct reduction of chloral hydrate in water with sodium borohydride. Suggest a mechanism for this reaction. Take note that sodium borohydride does not displace hydroxide from carbon atoms!
PROBLEM 9
It has not been possible to prepare the adducts from simple aldehydes and HCl. What would be the structure of such compounds, if they could be made, and what would be the m compounds be made?
Problems for Chapter 7
PROBLEM 1
Are these molecules conjugated? Explain your answer in any reasonable way.
PROBLEM 2
How extensive is the conjugated system(s) in these compounds?
PROBLEM 3
Draw diagrams to represent the conjugation in these molecules. Draw two types of diagram: (a) Show curly arrows linking at least two different ways of representing the molecule (b) Indicate with dotted lines and partial charges (where necessary) the partial double bond (and charge) distribution.
PROBLEM 4
Draw curly arrows linking alternative structures to show the delocalization in (a) diazomethane CH 2 N 2 (b) nitrous oxide, N 2 O (c) dinitrogen tetroxide, N 2 O 4
20 Problems to accompany Organic Chemistry
PROBLEM 5
Which (parts) of these compounds are aromatic? Justify your answer with some electron counting. You may treat rings separately or together as you wish. You may notice that two of them are compounds we met in problem 2 of this chapter.
PROBLEM 6
The following compounds are considered to be aromatic. Account for this by identifying the appropriate number of delocalized electrons.
